Custom context in callback handlers

[Alexander4]

Hello,

I would like to request a feature to be added to the STM32 HAL.

Would it be possible to be able to add a custom user context when registering peripheral callbacks.

Example:

HAL_StatusTypeDef HAL_SPI_RegisterCallback(SPI_HandleTypeDef *hspi, HAL_SPI_CallbackIDTypeDef CallbackID, pSPI_CallbackTypeDef pCallback, void* UserContext);

And then as callback function:

typedef void (*pSPI_CallbackTypeDef)(SPI_HandleTypeDef *hspi, void* UserContext);

I really miss this feature and have had to code around it for god knows how many times.

I have added it myself to the SPI driver, but if I regenerate its all gone ofc.

So it would be real nice if this could be added to drivers.

Thx,

Alexander

[Andrew Neil]

This has been requested before:

Recently (Oct 2024): https://community.st.com/t5/stm32-mcus-embedded-software/feature-request-pass-arbitrary-data-pointer-in-hal-callbacks/m-p/727806

Older (May 2021): https://community.st.com/t5/stm32-mcus-products/is-there-a-way-to-provide-context-pointer-to-hal-callback/m-p/182064

PS:

Apparently being "tracked internally" by @mƎALLEm:

https://community.st.com/t5/stm32-mcus-embedded-software/feature-request-pass-arbitrary-data-pointer-in-hal-callbacks/m-p/728270/highlight/true#M55730

[Pavel A.]

> I have added it myself to the SPI driver, but if I regenerate its all gone 

To avoid losing your changes in the HAL libraries:

- When you use Cube to (re)generate code, select the option to create links to the libraries instead of copying all the files into your project. 

- Check your changes in the ST libraries into your version control (yes, make your private branch).

To minimize code differences, do not pass the UserContext as a new argument. Instead, add it to the SPI_HandleTypeDef struct. Then your callbacks will get this arg from the hspi pointer: hspi->UserContext.

[Andrew Neil]

---

@Pavel A. wrote:

To minimize code differences, do not pass the UserContext as a new argument. Instead, add it to the SPI_HandleTypeDef struct.

---

@Alexander4 there was some discussion of this in the 2021 thread:

https://community.st.com/t5/stm32-mcus-embedded-software/is-there-a-way-to-provide-context-pointer-to-hal-callback/m-p/182064

[mƎALLEm]

---

@Andrew Neil wrote:

This has been requested before:

Recently (Oct 2024): https://community.st.com/t5/stm32-mcus-embedded-software/feature-request-pass-arbitrary-data-pointer-in-hal-callbacks/m-p/727806

Older (May 2021): https://community.st.com/t5/stm32-mcus-products/is-there-a-way-to-provide-context-pointer-to-hal-callback/m-p/182064

PS:

Apparently being "tracked internally" by @mƎALLEm:

https://community.st.com/t5/stm32-mcus-embedded-software/feature-request-pass-arbitrary-data-pointer-in-hal-callbacks/m-p/728270/highlight/true#M55730

---

Escalated as well..

[unsigned_char_array]

I agree it should have been added to the function argument or to the handler struct.

Alternatively you can create a mapping table.

Some pseudocode:

typedef void (*usercallback_t)(SPI_HandleTypeDef *hspi, void* usercontext);

typedef struct
{
  void *peripheral;
  void *usercontext;
  usercallback_t function;
} usercontext_mapping_t;

static usercontext_mapping_t mappingtable[N];

void callback(SPI_HandleTypeDef *hspi)
{
  if (hspi == NULL) return

  for(int i=0;i<N;++i)
  {
    if(mappingtable[i].peripheral == hspi->instance)
    {
      if (mappingtable[i].function != NULL)
      {
        mappingtable[i].function(hspi, mappingtable.usercontext);
      }      
      break;
    }
  }
}

Create a wrapper function around HAL_SPI_RegisterCallback that automatically registers the function and adds user context to the table. You can also wrap the deregister function.

I prefer creating wrapping functions over rewriting part of the functions. While it adds some overhead in terms of stack and CPU time that usually is not a problem. Once it becomes a problem I would switch from HAL to LL and write my own library.